1. Field of the Invention
The present invention relates to a printing technology for printing images by discharging ink onto a printing medium.
2. Description of the Related Art
In recent years, printing apparatuses (hereinafter ‘inkjet printers’) that print images by forming ink dots on a printing medium through the discharge of ink droplets have become widely used as image output apparatuses. Multiple nozzle groups that discharge various colors of ink are disposed on the print head of such an inkjet printer, and images are printed through the discharge of ink from each nozzle onto a printing medium.
There is a demand for faster printing capability to accommodate large volume jobs, and printing media of larger formats. In order to respond to this demand, bidirectional printing, in which ink dots are formed during both the forward and reverse paths of the print head's movement over the print medium during main scanning, has been developed and is currently available.
When bidirectional printing is executed, the order of ink drop discharge from the print head with respect to a given pixel is different during forward path main scanning and reverse path main scanning. For example, let us consider a situation in which a print head is used containing four nozzle groups that discharge ink in the four colors of black (K), cyan (C), magenta m and yellow (Y) and are aligned in the order of KCMY as viewed in the direction of the forward path of main scanning. During forward path main scanning, with respect to a given pixel, ink is discharged in the order of YMCK. During reverse path main scanning, ink is discharged in the reverse order of KCMY with respect to a given pixel. If the order of ink discharge is different for the different colors of ink, the order in which the different colors of ink permeate the print medium also changes. Therefore, even if the same amount of ink is discharged for each color, the resulting hue will be slightly different for each pixel. As a result, even if the same amount of ink is discharged, the dots formed during forward path main scanning will have a different hue than dots formed during reverse path main scanning. When bidirectional printing is executed, the regions in which the order of ink discharge is different become conspicuous and color unevenness is perceived.